This comprehensive textbook, spearheaded by the Sleep Research Society, presents an in-depth exploration of sleep and circadian science The book commences by defining sleep and circadian rhythms and discussing various research methods employed in the field. It summarizes the current understanding of brain mechanisms, physiology, and genetics related to sleep and circadian rhythms, as well as their ontogeny and phylogeny. The text also examines the evidence supporting the restorative functions of sleep for both the brain and the body. Finally, it delves into the pathophysiology and demographics of major sleep disorders, the effects of sleep loss on performance and safety, and relevant sleep health policies. Authored by renowned experts in the field, the content provides a succinct summary of the current understanding of sleep and circadian rhythms, making it an ideal resource for upper-level undergraduate and introductory graduate courses. Additionally, the book serves as an invaluable reference for physicians seeking certification in Sleep Medicine and caters to individuals interested in gaining a scholarly understanding of sleep and circadian science.